import java.util.Scanner;

public class Main {
    public int StrToInt(String str) {
        int sign=1;
        long sum=0;
        for(int i=0;i<str.length();i++){
            char ch=str.charAt(i);
            if(ch==' '){
                continue;
            }else if(ch=='-'){
                sign=-1;
            }else if(ch=='+'){

            }else if(ch>='0'&&ch<='9'){
                sum=sum*10+(ch-'0');
            }else{
                return 0;
            }
        }
        return (int)(sign*sum);
    }















    public int StrToInt1(String str) {
        int len=str.length();
        int sum=0;
        int i=0;
        while (i<len){
            while (i<len&& (str.charAt(i)<='0'||str.charAt(i)>'9')){
                char ch=str.charAt(i);
                if(sum!=0){
                    return 0;
                }
                if(ch=='+'||ch=='/'||ch=='-'){
                    i++;
                }else{
                    return 0;
                }
            }
            while (i<len){
                sum=(sum*10)+(str.charAt(i)-'0');
            }
        }
        return sum;
    }















    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        while (scanner.hasNext()){
            int col=scanner.nextInt();
            int row=scanner.nextInt();
            int[][] grid=new int[row][col];
            for(int i=0;i<row;i++){
                if(i%4==0||i%4==1){
                    for(int j=0;j<col;j++){
                        if(j%4==0||j%4==1){
                            grid[i][j]=1;
                        }
                    }
                }else{
                    for(int j=0;j<col;j++){
                        if(j%4==2||j%4==3){
                            grid[i][j]=1;
                        }
                    }
                }
            }
            int count=0;
            for(int i=0;i<row;i++){
                for(int j=0;j<col;j++){
                    count+=grid[i][j];
                }
            }
            System.out.println(count);
        }
    }
}
